In general, diesel engines are notorious as a major source of environmental contaminants such as NOx and fumes. However, no effective measures have been accomplished for solving those problems. It is known that these problems are due to the incomplete combustion in the engine occurring because of inadequate mixing of air and fuel. To solve these problems, swirl-aided combustion systems are commonly used. Here is one example for tackling this problem, which is disclosed in Japanese Patent Laid-open Application No. 07-97924. Referring to FIG. 10, the known combustion chamber fitted with a swirl chamber will be described:
In FIGS. 10A and 10B the right-hand side (toward the central axis 103) is called “rearward”, and the left-hand side (toward the cylinder liner 104) is “forward” each as designation for convenience only. The known combustion chamber shown in FIGS. 10A and 10B is provided with a cylinder 101 having a cylinder head 105, a reciprocating piston 102, and a combustion chamber 109. In addition, the cylinder head 105 is provided with a recess 106 in which a mouthpiece 107 is fitted. The mouthpiece 107 is provided with a top-open recess 107a, and t15he recess 106 includes a bottom-open recess 106a. The top-open recess 107a and the bottom-open recess 106a constitute a space 108 functioning as a swirl chamber, hereinafter the space being referred to as “swirl chamber 108”. The swirl chamber 108 communicates with the combustion chamber 109 through a main nozzle hole 111 having a center axis 113. The main nozzle hole 111 is forwardly inclined toward the swirl chamber 108. The mouthpiece 107 is additionally provided with a pair of sub-nozzle holes 102  112, through which a secondary air is forced into the swirl chamber 108 on the compression stroke. The sub-nozzle holes 112 are symmetrically positioned on opposite sides of the central axis 113-114 as shown in FIG. 10A.
Under the construction mentioned above, however, a major disadvantage is that the second air ejected through the sub-nozzle holes 112 does not reach the central part of the swirl chamber 108, thereby failing to bring about effective swirls therein. In this way the conventional sub-nozzle holes 112 are not conducive to the full utilization of the secondary air.
The disadvantages mentioned above is due to the following arrangement of the sub-nozzle holes 112: When a hypothetical sphere 115 is supposed about the center 107c of the open end 107b of the top-open recess 107a, and the radius of the open end 107b and that of the sphere 115 are respectively supposed to be 100% and 70%.
The sphere 115 having a radius of 70% passes outward, whereas the sphere 115 having a radius of 50% passes inward in FIGS. 10A and 10B. In this situation, the central axis 112a-112b of each of the sub-nozzle holes 112 passes outside the sphere 115.
In another aspect, when the mouthpiece 107 is seen from just above, the sub-nozzle holes 112 have their upper openings 112c deviated from the center of the swirl chamber 108 so that even if every sub-nozzle hole is oriented vertically, the central axis 112a-112b of each sub-nozzle hole 112 cannot pass inside the 50% sphere 115.
Accordingly, an object of the present invention is to provide an improved swirl chamber capable of causing effective swirls to help air and fuel being well mixed, and dispersing the fuel well in the swirl chamber.
Another object of the present invention is to provide an improved swirl chamber capable of reducing the production of both NOx and fumes, not one or the other under the conventional system.